A stretched fuse device

ABSTRACT

A stretched fuse device comprising a brass wire made of 45 to 48 percent of zinc and copper as the remainder with a Beta phase accounting for more than 90 percent of said alloy, said fuse being stretched in introducing electric current therethrough, wherein the cutoff of said fuse enables, if necessary, either or both of the closure of an alarm circuit and the indication of said cutoff to be effected.

United States Patent 1191 Kawazoe [54] STRETCHED FUSE DEVICE [75]Inventor: Toshinohu Kawazoe, Tokorozawa,-

Japan [73] Assignee: Nippon Denzai, Ltd., Gunna ken, Japan 22 Filed:Feb.4, 1972 [21] Appl. No.: 223,626

[52] U.S. Cl ..337/290, 337/239 [51] Int. Cl. ..H0lh 85/36 [58] Field ofSearch ..337/190, 238, 239, 240, 290;

[56] v. 7 References Cited UNITED STATES PATENTS Horton ..337/239 113,710,297 14 1 Jan. 9 1973 3,510,819 5/1970 Smith ..337/190 X FOREIGNPATENTS OR APPLICATIONS 156,300 12/1920 Great Britain ..337/239 PrimaryExaminer-Hemard A. Gilheany Assistant Examiner-D. A. ToneAttorney-George B. Oujevolk [57] ABSTRACT A stretched fuse devicecomprising a brass wire made of 45 to 48 percent of zinc and copper asthe remainder with a B phase accounting for more than 90 percent of saidalloy, said fuse being stretched in introducing electric currenttherethrough, wherein the cutoff of said fuse enables, if necessary,either or both of the closure of an alarm circuit and the indication ofsaid cutoff to be effected;

2 Claims, 13 Drawing Figures PATENTEDJAR 9 I975 SHEET 1 [1F 4 PRQPORTION(2 w m m m T\ 3 M 0% 0 IO 0 c 2 o w FIG.2

TEMPERATURE (C) CONSTANTAN (#0 cm) TEMPERATURE (C) B BRASS ncm) F I G. 3

I PATENTEDJAI 9197a TIME SHEET 2 UF 4 SECONDS MINUTES 10000 8000 6000100 N LCDQO CURRENT PAIENTEUJ/m 9197s SHEET 3 BF 4 FIG. 5

o TENSILE STRENGTH FIG.6A

A STRETCIIED FUSE DEVICE BACKGROUND OF THE INVENTION This inventionrelates to a stretched fuse device and more particularly to a stretchedfuse device comprising a brass wire made of 45 to 48 percent of zinc andcopper as the remainder with a B phase accounting for 90 percent of thealloy(hereinafter referred to as a B brass wire"), said fuse beingstretched in introducing electric current therethrough.

Already known is a stretched fuse device wherein the fuse is stretchedin introducing electric current therethrough. When excess current passesthrough the fuse of such device, the fuse is generally cut off due tothe resulting high .loules heat. Where subjected to a normal tension,the fuse or the prior art device often presents a red-hot orincandescent state, that is a temperature of over l,000C when it is cutoff due to passage of excess current therethrough. Such high heat isconducted to a semiconductor element such as a transistor or diodeincluded in an electronic apparatus where said stretched fuse device isused, most likely resulting in the deteriorated properties of saidelement or sometimes its eventual destruction.

If, however, the fuse is stretched with a greater force so as to allowit to be cut off before reading a red-hot or incandescent state, thensaid large tension gradually will elongate thefuse even during theintroduction of rated current to give rise to the so-called creep cutoffwith the resultant failure to provide a fuse device capable ofdisplaying accurate current-time characteristics (that is, therelationship of the magnitude of the current and the time required forthe fuse to be cut off).

SUMMARY OF THE INVENTION It is accordingly the object of this inventionto provide a stretched fuse device having such mechanical strength as isfree from the effect of room temperature, capable of being cut off atsufficiently low temperatures to prevent semiconductor elements andorganic insulation materials from being'damaged by heat, and

moreovermaintaining a very accurate current-time relationship. 1

According to this invention, the above-mentioned object is attained by astretched fuse device which is prepared from a B brass wire consistingof 45 to 48 percent of zinc and copper as the remainder with a B'phaseaccounting for more than 90 percent of said alloy and is used as a fusein a stretched state when current is introduced.

BRIEF DESCRIPTION OF THE'DRAWINGS FIG. 4 is a curve diagram of thecurrent-time characteristics of a stretched fuse device according to theinvention prepared from a B brass wire;

FIG. 5 is a curve diagram illustrating the co-ordinate analytic methodused to obtain the curves of FIG. 4;

FIGS. 6A, 6B and 6C schematically indicate the manners in which the fuseof the invention is stretched;

FIG. 7A, 7B and 7C are respectively the lateral, cross sectional andplan views of a stretched fuse device according to an embodiment of theinvention; and

FIGS. 8A and 8B are respectively the plan and lateral views, partly insection, of a stretched fuse device according to another embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION The most important feature of thisinvention is that the fuse used in the invention consists of a B brasswire to utilize its unique physical properties, thereby obtainingdesired results. There will now be discussed the physical properties ofthe B brass before describing the preferred embodiments of theinvention. Brass material in general use contains less than 35 percentof zinc, that is, has an a phase, as shown in FIG. 1, presenting thephase condition of a Cu-Zn system. When the proportion of zinc increasesto around 40 percent, there appears a B phase, namely, a mixed phase (aB). Further when the zinc content rises to 45 percent, there onlyresults a B phase. When the zinc exceeds 50 percent, there occurs a 7phase. Upon appearance of the 7 phase, the brass sharply becomesbrittle, failing to display physical processability, for example, wiredrawing.

There is given in Table 1 below the physical con stants at normaltemperature of B brass according to this invention which consists of 45to 48 percent of zinc and copper as the remainder with a B phaseaccounting for more than 90 percent.

TABLE I Melting point (C) 870 Density (g/cm") 8.4 Young's modulus ofelasticity (dyne/cm) ll l0 Tensility (kg/mm") to Linear expansion(cm/"C) 19x10 Heat conductivity (w/cm C) 0.6 Specific heat (cal/g/C)0.09 Specific resistivity (pfl cm 5.610.] Resistivity-temperaturecoefficient (0 to C) 2.3Xl0' The present inventor conducted experimentswith brass having such physical properties. Namely, a sample ofB brassconsisting of 45 to 48 percent of zinc and copper as the remainder witha B phase accounting for more than 90 percent was repeatedly subjectedto low temperature annealing at 350i50C during a wiredrawing process. Asa result, he has discovered that this operation enabled the structure ofsaid B brass to be formed into a fibrous state, making it possible todraw the metal into a very fine wire 0.06 mm in diameter.

It has been further found that a B brass wire thus prepared displayed anorder-disorder transition at a relatively low temperature of 454 to 468Cand that this type of B transition acted very effectively for the reasongiven below when said wire was used as a fuse for the subject stretchedfuse device. The most prominent physical feature of the B brass of thisinvention is that it indicates an order-disorder transition at presentsa disorderly lattice form where the atoms of copper and zinc arearranged at the lattice points in an irregularly mixed state. The Bbrass exhibits due to said order-disordertransition unique variations inits physical properties which can not be observed in other single metalsor alloys.

FIG. 2 shows the relationship of the tensile strength and temperature ofthe B brass compared with that of constantan. The constantan used inthis test was a solid solution alloy consisting of 43 to 46 percent ofnickel and copper as the remainder. FIG. 3 illustrates'therelationshipvof the electric resistance and temperature of the B brasscompared with that of constantan. As apparent from FIG. 2, a solidsolution alloy, for example, constantan generally presents aprogressively increas ing linear decline in tensile strength astemperature rises. In contrast, the B brassis reduced in tensilestrength to a smaller'extent than constantan over a tema more prominentdecline of tensile strength at around 250C, and at 450C as small atensile strength as 2 kg/mm corresponding to about one-fortieth of 80kg/mm at normal temperature.

As seen from FIG. 3, the specific resistivity of the B brasssubstantially linearly increases up to around 300C, but nonlinearlyrises at higher temperatures and reaches at 470C 16 to 17 O. cm, a valueabout three times that which occurs at normal temperature.

As previously mentioned, when there passes excess current through a Bbrass wire, its electrical resistance grows larger due to temperaturerise resulting from Joule s heat. Since the increase of temperature andthat of electrical resistance synergetically act on each other,

, the B brass wire displays a sharply rising temperature.

On the other hand, its tensile strength begins to decrease prominentlyat around 2009C. If therefore, a

fuse made of a B brass wire is used in a stretched state,

the wire neverfails tobe cut off in an extremely short time at lowertemperatures than 400C due to the heat generated by passage of excesscurrent.

Table 2 below gives the rated current, the cut load and electricresistance at normal temperature, the

operating'tension, the ratio of said tension to the cut load and thefuse characteristics of a B brass wire according to this invention whereit was used with a stretched fuse device shown in FIGS. 7A, 7B and 7C.

TABLE 2 go aa FIG. 4 shows the current-time characteristics of B brasswires of this invent-ionhaving the various diameters shown in Table 2above, where there was actually introduced rated current of0.5 to amp.therethrough. The figure indicates that said wires were very sensitivelycut off to-excess current higher than the rated cur rent.

It will be apparentfrom the foregoing description that when there wasintroduced current'through a B brass wire according to this inventionconsisting of 45 to 48 percent of zinc and copper as the remainder witha B phase accounting for more than 90 percent while it was keptstretched, then said brass wire could provide a stretched fuse devicehaving very accurate currenttime characteristics.

' perature range of from normal to 200C, and indicates The curve diagramof FIG. 4 shows that a stretched fuse device using the B brass wire ofthis invention displayed prominently excellent current-timecharacteristics. For better understanding of the invention,

there will now be given a theoretical analysis in supplemerit to theforegoing qualitative description of the invention by reference to thecurve diagram of FIG. 4

using meansderived from the co-ordinate analytical method. 7

The current-time characteristics of general stretched fuse wires may beobtained by resolving simultaneous equations consisting of the followingequations (1) and u =fl (n 'r g(u) (2) The equation (1) denotes atemperature-time curve and the equation ('2) a tensilestrength-temperature curve. In the above equations, u representstemperature (C), t time (sec.), and r a tensile strength (g). Since theequations (1) and (2) are associated with nonlinear values, there arepresented considerable difficulties in resolving said equations (1) and(2) simply by calculation. For practical purpose, therefore, resolutionby the co-ordinate analytical method is more advisable.

There will now be explained by reference to FIG. 5 the drawing procedureof the co-ordinate analytical method. First, with current value i, (n=aninteger) taken as'a parameter, a curve representing the equation isdrawn in thefirst quadrant to indicate atime-tem- =rr( o (4) associatedwith the relationship of the cutoff tension and time of a fusedetermined by its material and diameter to show a temperature-tensilestrength relationship From the two curves associated with the aboveequations (3) and (4) there can be determined the currenttimecharacteristics of a fuse wire in the following manner. Let it beassumed that there is applied a tension r,(0 r, 7 on the fuse wire. Here1' is taken to represent a tension applied in said fuse wire when it iscut off at normal temperature.

Referring to FIG. 5, there is plotted in the 1 axis of the secondquadrant 01', as representing the magnitude of a tension 1", applied onthe fuse wire. With u taken to designate the intersection of a linedrawn from 'r, in parallel with the ordinate and a curve denoting thetemperature-tensile strength relationship u-r l d d then u denotes thetemperature at which the fuse wire is cut off when subjected to thetension 1,. Therefore, with t, to t taken to denote the intersections ofa straight line drawn parallel with the abscissa through point u and thetime-temperature curves of the first quadrant obtained when there wasused current having magnitudes of i, to i then said intersectionsindicate the lengths of time required for the fuse wire to be cut offupon introduction of current having said magnitudes. Further, there aredetermined intersections between straight lines drawn parallel with theordinate through the aforesaid intersections t, to i and straight linesdrawn parallel with the abscissa through points i to 0 i of the fourthquadrant which are taken to indicate the magnitudes i to 1' of current.The first mentioned intersections defined by both groups of straightlines are connected to draw a curve S. Then this curve S shows thedesired current-time characteristics of the fuse wire.

As apparent from the above-mentioned co-ordinate analytic method, thecurrent-time characteristics of a stretched fuse wire may be expressedby the following equation:

i= Mr) 5) The value of this equation is determined by resolving thefollowing simultaneous equations:

Since the equation (6) can be determined from FIG. 3 and the equation(7) from FIG. 2, it will be apparent that unique variations in thephysical properties of a B brass wire due to its order-disordertransition exert a very effective action when said wire is used as astretched fuse.

The process of stretching the B brass wire of this invention used with astretched fuse device may be illustrated for example, by those of FIGS.6A, 6B and 6C. FIG. 6A indicates the process fitting a spring (notshown) to each end of a fuse wire and stretching it by applying a forcethereto acting in opposite directions indicated by the arrows A and Bwith this process, the springs are brought back to the originalcondition when the fuse wire is cut off, so that if required, one of thesprings can be used in its original position to close a circuit forgiving an alarm on the cutoff of the fuse wire and the other spring canbe used to indicate the cutoff itself.

FIG. 6B shows the process of fixing one end of the fuse wire andconnecting a spring (not shown) to the other end so as to stretch thewire only in the direction direction intersecting the fuse wire, forexample, at

right angles thereto, so as to be stretched as a whole.

Among the above-mentioned processes, those of FIGS. 6A and 68 cause thecutoff portions of the fuse wire to be instantaneously separated,offering the prominent effect of extinguishing an are which mightotherwise occur, for example, at the time of short-circuiting.Accordingly, a stretched fuse device using a fuse wire stretched by theprocess of FIG. 6A or 68 can obviously have a cutoff capacity severaltimes larger than that of a nonstretched fuse device.

There will now be described the actual application of a stretched fusedevice according to this invention. FIGS. 7A, 7B and 7C jointlyrepresent a stretched fuse device used to protect the relay circuit ofan automatic telephone exchange mechanism. There is a concrete exampleof the process of stretching a fuse wire with two springs, namely, thatof FIG. 6A. The body 1 of said fuse device is integrally formed ofsynthetic resin, for example, polyvinyl chloride. At the lengthwise endsare formed deep cavities 4 and 5 to receive contact terminals 2 and 3made of elastic metal. The terminals 2 and 3 are so fitted to the devicebody I as to close the opening of the cavities 4 and 5 by means ofholding metal parts 8 and 9 bored with plug holes 6 and 7 withelectrical contact maintained therewith. One end of one holding metalpart 8 extends into a recess 10 formed in the device body 1. To the endof said extended portion of the holding metal part 8 is fitted a coilspring 11, one end of which is soldered to the holding metal part 8 andthe other free end of which is provided with a tubular indicator 12 madeof sybnhetic resin. The device body 1 further has an aperture 13 open atone end to the recess 10 and lined with an insulation tube 14 made of,for example, phenol resin. One contact terminal 3 extends beyond theouter opening of said aperture 13. The free end of the coil spring 11also extends beyond the inner opening of said aperture 13, though in theopposite direction. The extended portions of the contact terminal 3 andcoil spring 11 are soldered to the B brass wire 14 having theaforementioned physical properties which is inserted into the aperture13 so as to cover both openings of the aperture 13. Said contactterminal 3 and coil spring 11 thus soldered to the B brass wire impact atension thereto. A stretched fuse device constructed as described aboveis used under the condition in which the plugs of a socket means areinserted into the plug holes 6 and 7 and the contact terminals 2 and 3brought into electrical contact with said plugs.

There will now be described the operation of the stretched fuse deviceillustrated in FIG. 7. A B brass wire through which there is to beintroduced rated current of 0.5 amp, has, as shown in Table 2, adiameter of 0.071 mm and is operated with a tension of 1 10 g whichaccounts for 28.2 percent of a cutoff load. While there flows throughthe B brass wire rated current, that is, current having 0.5 or smalleramperes, the wire does not present any creep cutoff resulting from itsexcess extension, because the operating tension has as small a value as28 percent of the cutoff load, enabling a stretched fuse device usingsaid wire to he operated under a very stable condition.

Where the B brass wire 14 receives excess current of, for example, 1ampere, its temperature sharply rises due to the resulting .loules heat,leading to its increased electrical resistance as shown in FIG. 3. The

greater the electrical resistance, the more prominent the Joules heattovaccelerate the temperature rise of the B brasswire 14. As a result,the wire 14 begins to be sharply reduced in tensile strenght at around200C and is cut off at themoment the tensile strength falls to below theoperating tension. As seen from FIG. 2, the wire 14 has extremely smalltensile strength at around 400C, so that the temperature at which it iscut off is absolutely prevented from exceeding 400C. Accordingly, evenwhen there is fitted to electronic appliances using semiconductorelementsa stretched fuse device consisting of a B brass wire accordingto this invention which is subjected to an operating tension accountingfor to 30 percent of its cutoff tension, it never happens that thesemiconductor elements are deteriorated in property or fully damaged byheat generated from the device when-the fuse is cut off. According tothe stretched fuse device of this invention, when the B brass wire 14 iscut off by passage of excess current therethrough, the cutoff portionsof the wire 14 are instantaneously separated, as previously described,from each other by the action of the coil spring 11 and the elasticityof the contact terminal 3, so that said device has a cutoff capacityseveral times larger than that of a nonstretched fuse device. Furtherupon the cutoff of the wire 14, the free end of the coil spring isbrought back to its original position shown in FIG. 78, causing theindicator 12 to project from the-device body 1, showing that the fusehas been cut off. At the same time, the free end of the contact terminal3 regains its original position to be pressed against the contactterminal of an alarm circuit (not shown) to close itfor actuation. I

FIGS. 8A and 8B jointly denote -a stretched fuse device using a B brasswire stretched by the process of FIG. 6B. To a substrate 40 is movablyattached an insulation support pipe 43 by fitting metal parts 41 and 42.One end of the support pipe 43 is fitted into a fixed terminal metalpart 44. A fitting metal part 45 placed on the inner bottom wall of themetal part 44 supports one end of a B brass wire 46, the other end ofwhich is fitted to a fitting metal part 48 disposed at one end of a leadwire 47 inserted into the insulation support pipe 43. Theother end ofthe lead wire 47 is fixed to the fitting metal part 42 in a stateengaged with the outer end of the insulation support pipe 43. Near theouter end of said pipe 43 is formeda flange 50. Across the flange 50 andfitting metal part 42 is stretched an extensible coil spring 51 woundabout the pipe 43 so as normally to urge the pipe 43 to the right sideof FIG. 8A. Accordingly, the B brass wire 46 is normally stretched tothe right side as indicated by thecoil spring'51.

The embodiment of FIGS. 8A and "8B is adapted to against the metal part41. If, therefore, the insulation support pipe 43 is so designed as tohave its outer'end projected outside ofa cover (not shown onl when thepipe 43 IS made to move, then the cuto oft e wire 46 will be indicated.

If, in the embodiment of FIG. 8, there is connected an alarm circuit(not shown) between the metal parts 41 and 42, said circuit can beeasily actuated when the outer end of the insulation support pipe 43projects outside of the cover.

If a B brasswire according to this invention is plated in advance withcorrosion resistant metal such as nickel, silver, cadmium or tindepending on the kind of an ambient atmosphere in which said'wire isused, there can be prevented the unnecessary cutoff of the wire due tocorrosion.

It will be apparent that though the foregoing embodiments only indicatepart of the applications of the stretched fuse device of this invention,"there may be taken, forexample, various processes of stretching thefuse wire, actuating an alarm circuit or indicating its cutoffwithout-departing from the principle of the invention.

What is claimed is:

1. In a stretched fuse device having a fuse wire stretched inintroducing current therethrough, the improvement being that said fuseis a'brass wire consisting of 45 to 48 percent of zinc and copper astheremainder with a B phase accounting for more that percent of the alloy.

2. The stretched fuse device according to claim 1 wherein the brass wireis plated with at least one metal of the group consisting of nickelsilver, cadmium and tin.

2. The stretched fuse device according to claim 1 wherein the brass wireis plated with at least one metal of the group consisting of nickelsilver, cadmium and tin.